If you need to install or update an Arch Linux package and you are behing a proxy, there is a way to quickly configure it to use that proxy.
This will not be permanent, so it is great to use with Laptops, to set a momentary proxy server.
To set the http proxy enter in the console
To switch to root, as root is the user that is able to run pacman
To set the ftp proxy enter in the same console window
be sure to use the appropriate IP and port according to your environment.
Thanks to the comment below, I have noticed that this was missing, here is the answer to that comment:
Enter the correct username, password, IP and port.